This invention relates to a process for the liquefaction of solid carbonaceous materials. More particularly, this invention relates to such a process wherein molecular nitrogen is separated from molecular hydrogen.
As is well known, coal has long been used as a fuel in many areas. For several reasons, such as handling problems, waste disposal problems, pollution problems and the like, coal has not been a particularly desirable fuel from the ultimate consumers point of view. As a result, oil and gas have enjoyed a dominant position from the standpoint of fuel sources throughout the world.
As is also well known, proven petroleum and gas reserves are shrinking throughout the world and the need for alternate sources of energy is becoming more and more apparent. One such alternate source is, of course, coal since coal is an abundant fossil fuel in many countries throughout the world. Before coal will be widely accepted as a fuel, however, it is believed necessary to convert the same to a form which will not suffer from the several disadvantages alluded to previously.
To this end, several processes wherein coal is either liquefied and/or gasified have been proposed heretofore. Of these, the processes wherein coal is liquefied appear to be more desirable in most cases since a broader range of products is produced and these products are more readily transported and stored. In such liquefaction processes, the coal is first slurried with a suitable solvent or diluent and then contacted with molecular hydrogen at an elevated temperature and pressure. Generally, the reaction product comprises a relatively high BTU gaseous product, a liquid product and a bottoms product. The bottoms will contain unconverted coal and inorganic mineral matter which was originally contained in the coal.
In the processes which have been proposed heretofore, molecular hydrogen may be produced by reforming the hydrocarbon portion of the gaseous product from the liquefaction step. Hydrogen may also be produced by gasifying the bottoms product either directly or by first coking the bottoms product and then gasifying the coke thus obtained. When coking is employed, a gas of relatively high BTU content can also be produced and this, too, may be reformed to produce molecular hydrogen. Generally, the hydrogen thus produced will be suitable to effect the liquefaction. In a closed system, however, and when air is used in the bottoms upgrading operation, nitrogen will build up in the hydrogen stream. In order to maintain hydrogen purity, and hence, maximum operating efficiency, it is, therefore, necessary to separate molecular nitrogen from the hydrogen to be used during liquefaction.